1. Field of the Invention
The present invention relates to a mass analyzing apparatus including an ion trap and a time-of-flight mass spectrometer.
2. Description of the Related Art
Recently, a mass analyzing method has come into widespread use as a principal analyzing method in the fields of bioengineering and biochemistry. Such a trend is primarily attributable to development and improvement of ionization techniques and mass spectrometers adapted for applications to the biotechnological field.
As the ionization techniques, two ionization processes have been developed which are capable of directly and stably ionizing a thermally unstable sample molecule to be measured, which has a high molecular weight. One process is ESI (electrospray ionization) capable of directly taking, as an ion, a measured sample dissolved in a solution in an atmosphere. The other process is MALDI (matrix-assisted laser desorption ionization) that ionizes a sample molecule by irradiating a laser beam to the sample molecule. Those two ionization processes give an operator of the measurement different kinds of information, and hence they are employed in a complementary way in the biotechnological field.
Also, as a mass spectrometer adapted for applications to the biotechnological field, a time-of-flight mass spectrometer (TOF) is employed in many cases for the reason that a sample to be measured has a large molecular weight. With the recent progress of electronics, the TOF has become a more popular apparatus and its applications to a wide range including the biotechnological field are expected.
Because of having high sensitivity, a mass spectrometer in combination of the soft ionization process, such as ESI or MALDI, with the TOF has rapidly become widespread as an analytical technique in the biotechnological field. In many cases, however, an ion produced by the soft ionization process is a pseudo molecular ion (M+H)+ in which a molecule is ionized with addition of a proton H+ to the molecule. This fact has raised the problem that a measured mass spectrum provides only information of molecular weight, and hardly provides information regarding the molecular structure.
In order to overcome such a deficiency of information regarding the molecular structure, it has been proposed to provide an ion trap between an ESI ion source and the TOF such that mass measurement can be performed with high accuracy and an MSn analysis can be realized. This proposed process is disclosed in JP,A 2001-297730 (Patent Reference 1). The provision of the ion trap between the ESI ion source and the TOF makes it possible to repeat isolation or dissociation of an ion within the ion trap, and to realize the MSn analysis. The ion expelled out of the ion trap is introduced to an ion acceleration section of the TOF and is accelerated in a perpendicular direction in sync with the introduction of the ion. High accuracy in mass measurement can be achieved with an arrangement that the direction in which the ion is introduced is set perpendicular to the direction in which the ion is accelerated.